Miniaturization and harmonic suppression rat-race coupler using C-SCMRC resonators with distributive equivalent circuit

This letter describes a miniaturized spurious pass-band suppression rat-race coupler using compensated spiral compact microstrip resonant cell (C-SCMRC) resonators. A distributive equivalent circuit model is proposed for circuit synthesis. The C-SCMRC resonator has been simulated by the equivalent circuit and method of moments (MoM) method. The measured results have good agreement with the simulated ones. The circuit area of the proposed rat-race coupler is only 45% of the conventional coupler. Furthermore, experimental results show that the coupler suppressed the second and third harmonic signals, -32.5dB and -22.5dB.